Pre-heat oven to 300 F degrees.
In gallon-sized zip-top bag, add sweetener, cocoa powder, cinnamon and collagen powder. Seal and toss around until combined.
In large microwave save bowl, add nut butter and chocolate and microwave in 30-second increments until chocolate melted. Use spatula to stir together until smooth.
Add cereal and gently stir with spatula taking care not to crush up.
Add coated cereal to zip top bag with dry ingredients. Seal bag and shake until all contents are stuck onto cereal.
Spread mixture out on foil or parchment-lined rimmed baking sheet and bake in center rack for 25 - 30 minutes, using spatula to turn up and redistribute contents halfway through cooking.
Remove from oven and let cool for 10 minutes on baking sheet. Break up any big clumps and store in air-tight container after completely cooled. May be stored on the counter for up to a week.